DC (Direct Current)-to-DC converters may be found in many electronic devices. For example, DC-to-DC converters are often found in PDAs (Personal Digital Assistant), cellular phones and laptop computers. These electronic devices often contain several sub-circuits with different voltage level requirements from that supplied by a battery or an external supply. A DC-to-DC converter converts a source of direct current from one voltage level to another voltage level in order to meet the voltage levels required by sub-circuits.
One method of providing DC-to-DC conversion is through the use of a voltage divider. A voltage divider uses two resistors in series to drop a higher voltage to a lower voltage by “dividing” the higher voltage between the two resistors. A voltage divider, however, may dissipate too much power for devices such as laptop computers and cell phones.
Electronic switch-mode DC-to-DC converters convert one DC voltage level to another by storing the input energy temporarily and then releasing that energy to the output at a different voltage. The storage may be in either magnetic field storage components (inductors, transformers) or electric field storage components (capacitors) or a combination of both. This conversion method is more power efficient (often 75% to 98%) than a voltage divider for example. This efficiency is beneficial to increasing the running time of battery operated devices.
The efficiency of electronic switch-mode DC to DC converters has increased due, in part, to the use of power FETs (Field Effect Transistors), which are often able to switch at high frequency more efficiently than other switching devices. One reason that power FETs may increase the efficiency of DC-to-DC conversion is that power FETs can have low “on” resistance. Having low “on” resistance reduces the power lost when power FETs are switching.
Power FETs may be rendered inoperable when too much current is conducted through them. For example, when a power FET starts to charge a discharged capacitor, the instantaneous current or surge current drawn through the power FET can be too great and cause the power FET to stop functioning. Detecting when a power FET is drawing too much current and then turning the power FET off for a period of time can stop the power FET from being rendered inoperable.